1. Field of the Invention
The present invention relates to an inkjet head using a so-called fill-before-fire method.
2. Description of Related Art
An inkjet head that ejects ink by an inkjet system includes therein nozzles from each of which ink is ejected; a common ink chamber that supplies ink to be ejected from each nozzle; and individual ink passages leading from the common ink chamber to the respective nozzles. When the inkjet head ejects ink, a pressure is applied to ink in a pressure chamber formed at a portion of each individual ink passage, and ink supplied from the common ink chamber is thereby ejected from each nozzle. At this time, a pressure wave is generated by applying the pressure to ink in the pressure chamber, and as a result, the proper oscillation of the pressure chamber is generated in the individual ink passage. Japanese Patent Unexamined Publication No. 2003-305852, particularly in FIG. 7 of the publication, discloses an inkjet head that efficiently ejects ink by using peaks of the proper oscillation. The inkjet head of the publication adopts a so-called fill-before-fire method in which the volume of each pressure chamber is once increased and then the pressure chamber is restored to its original volume after a predetermined time elapses, to apply a pressure to ink in the pressure chamber.
However, when an inkjet head using the fill-before-fire method as in the above publication ejects ink, some shapes of individual ink passages may cause a case wherein a tip portion of an ink droplet is split off from the main body of the droplet to form a high-speed small ink droplet. That is, some shapes of individual ink passages may cause a case wherein a split-off ink droplet impacts a printing paper at a different timing from that of the original ink droplet. This brings about a problem of degradation in the reproducibility of an image to be formed on a printing paper by the inkjet head.